Carbonization of lignite



United States Patent CARBONIZATION OF LIGNITE Fred Denig, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed Nov. 12, 1957, Ser. No. 695,792

2 Claims. (Cl. 208-8) This invention relates generally to the carbonzation of coal and more particularly to a method for carbonzation of lignite and low grade coals.

It is an object of the present invention to provide a method of carbonizing lignite and low rank coals in a manner such that there will result a coal tar by-product having the characteristics of high-temperature tars.

Coal tarsproduced during the carbonzation of coal are classified as either high-temperature tars or lowtemperature tars. Of these two classes only high-temperature tars are of commercial significance. These coal tars are of an extremely complex mixture of Organic compounds. The composition of the tar depends principally` on the temeprature of carbonzation, but it is also influenced to a lesser extent by the nature of the coal which is coked. High-temperature tars, the most important commercially, contain large proportions of aromatic compounds; phenols, cresols, naphthalene,`

benzene and its homologues, and anthracene. They are produced by the cracking of the primary tars which result from the break-down of the coal structure itself during carbonzation. The compositions of the latter are infiuenced to some extent by the coals from which they are produced, but it has been found that further heating tends to eliminate the difiierences and the final composition of the tar depends primarily on the conditions of decomposition. i i

Low-temperature 'carbonzation yields tars which are less severely altered and which contain paraffins and some dihydroxy phenols, in addition to cresols, xylenols, still higher phenols, and alkylated naphthalenes. The variations in the composition of these tars are much grater than in those produced at the higher temperatures, because of differences in the degree of cracking of the primary compounds. These low-temperature tars are substantially useless commercially. i

In the carbonzation of lignite and low rank coals for the' formation of coke suitable for use in the reduction of ores to produce a tar equivalent to that produced in high-temperature coke ovens the temperature at which the lignite is carbonized is about the same as the temperature required when carbonizing the high grade bituminous coal in conventional coke ovens.

Occasionally low-temperature carbonzation of lignite and low grade coal is required such that a sati'sfactory coke is produced, but theselow-temperature carbonzations have the drawback of producing a tar having the characteristics of a low-temperature tar.

In the carbonzation of coal in the conventional slottype coke oven the heat is applied to the coal through the outer coke oven wall. Coking proceeds from the oven wall to the vertical center of the coal charge. The entire coal charge is quickly coated by a layer of coke formed next to the heating walls and the gases and tars are forced through the coke mass against the hot walls and are further cracked giving a gas high in hydrogen content and the well known high-temperature tar at the oven gas outlet.

In one known method of carbonizing lignite, the lignite is nitially pulverized and then dryed. in a first unit containing a fiuidized bed and wheren the products of combustion of a specific amount of other lignite is charged through the unit. The hot solid lignite from the first unit is then fed to a second unit which is maintained at a higher temperature and contains another fluid 'ized bed. The treatment of charging the products of combustion of the lignite through the fluidzed bed as performed in the first unit is repeated. While the temperature in this second unit is maintained higher than the temperature in the first unit, this high temperature must sometimes be controlled such that it does not exceed the temperature at which the lignite breaks into powder and thereby fails to produce a suitable coke. These lower controlled temperatures result in a yield of a low-temperature tar. g

By the present invention it is proposed to carbonize the lignite and low grade coal' at the required temperatures for producing a coke suitable for the treatment of ore or the like, and also producing a tar having the characteristics of the aforementioned high-temperature tars.

Briefiy, this is accomplished by the proysion of a localized heating zone which is maintaned at a temperature which will convert the volatile matter driven oli during the carbonzation of the coke formation.

More particularly, the carbonzation of the lignite is accomplished with the assstance of electrical energy to provide a source of heat for the formation of coke and the volatile materials resulting therefrom the carbonzation are passed through a bed-of carbon or breeze coke which is also subjected to the electrical energy;

The above and further objects and novel features of the inventon will hereinafter appear morefully from the detailed description when the same are read inconjunction with the drawing. It is to be expressly understood, however, that the drawings are not to be a definiton of the invention but for the purpose of illustration only. i i i In the drawings where like parts are numbered alike; Fig. lis `a vertical section through a retort arranged to carry out the present invention. i i

In accordance with the present invention, there is used a convenient carbonzing oven which may be in the form of a retort having located therein means fol-conduct; ing electricalfcurrent therethrough for the purpose of providing the heat for carrying out theLcarbonz'ation.

The retort will be substantially filled with lignite or low grade coal, over the top of which will be superimposed a layer of carbonaceous material such azs coke breeze i for carrying out the method of the present and may be a steel retort 10 'of the type illustrated and disclosed in U.S. Patent 1,938,l21 issued to H. Stevens. For the purpose of Simplicity, only, the inner fire 'brick wall 11, upper end 13 and the hingedly connected bottom gate 15 are illustrated. It is to be understood, however, the retort 10 may be provided with fiues formed about the wall through which heat gases may be circulated as provided in the Stevens patent to assist in heating the i charge of lignite and rank coal to be carbo nized.

Disposed within the retort 10, for the purpose of providing an internal heating unit, is an electrode 17 of which the bottom end is in engagement with the bottom gate 15 and is connected to a low potential source of current and the upper end is connected to a high potential source of current. The electrode 17 may be formed of any P atented Feb. 1 1951 p,

Provided on the top 19 is a charging hole zl through which* the charge of material to be carbonzed 'is introduced into the' retort and atube 23 for taking* off the'` volatile constituents evolved duringthe carbonization of thecal.

The above described structure is similar to that described in the aforementioned Stevens patent. While the Stevens apparatus operates satisfactorily for the production of coke,-the temperatures created are such that lowtemperature tars'resu-lt therefrom, even when' high grade bituminous ores 'are carbonzed.

By the present invention there is provided a means for converting these low-temperature tars to high-temperature tars. To this end, high resistance clectrical-conductors, which may be in the form of carbon formed bricks 27, `are inserted in the brick wall 11 adjacent to the top 19. These bricks 27 are also connected to a source of current.

In carrying out the present invention the lignite charge L is ntroduced into the retort 10 until it reaches the level of the powdered carbon bricks 27. Thereafter a coke breeze 29 is introduced into the charging hole 21. The coke breeze 29 is dispersed and superimposed over the top of the lignite as a layer and contacts the' electrode 17 and the carbon bricks 27 thereby to form a porous surface electrode through which the vapors and gases driven off-during the carbonization may pass.

Upon the passage of current through the retort, the heat is supplied to the' charge of lgnite L by the flow of current through the electrode 17, whereupon the portion of the charge adjacent to the electrode 17 becomes heated and in this manner also becomes coke and a conductor having a slight resistance and afiords a greater clectrode diameter which in turn heats the next adjacent area and so on untl'the entire charge is heated.`

The evolved volatile substances in theform of vapors and gases during this carbonizaton stage arise from the lignite and pass upwardly through the layer of coke breeze 29 overlying the lignite. Since the coke breeze has a high resistance and is in contact with the electrode 17, the passage of current therethrough renders the coke breeze incandescent and creates a higher temperature than that of the underlying carbonization temperature. Hence, when the evolved gases pass through this localized hightemperature zone created by the layer of coal breeze 27, the volatile matter is further distilled such that substarces taken off' through the gas take-'oil tube 23 are converted to commercially usable` high-temperature tars.

Variations -andmodifications may-be made within the scope of the claims and portions of`the improvements may be used withoutothers.

1. A process for carbonizing and distilling lignite for forming coke and coal tar which comprises heating said lignite to drive ofi the volatile constituents and to' form coke; and passing said' volatile constituents` througha` localzed heating zone formed by electrically conductive carbon particles, passing an electrical current through said carbon particles to heat said zone to ncandescence to convert said' volatile constituents so that upon condensation said` volatile constituents form a coal tar having the characteristics of high-temperature tars.

2. A process for carbonizing and distilling lignite for` V forming coke and coal tar which comprises heating'the lignte by the passage of electrcal current therethrough incandescence whereby said zone a temperature substantially higher than` the temperature at which the lignte is formed into coke thereby to Convert said volatile constituents so that upon condens ation said' volatile constituentsform a coal tar having the characteristics of high-temperature tars.

ReferencesCitedin the file of this patent UNITED STATES PATENTS ,923,2`13` Karrick A 22,`19`3"3' ,937,552 Davis Dec.. s, 1933' 1,93s,12-1 Stevens Dec. 5, 1933` 2',573,9o6 Hua Nov. 6, 1951 2,71o;2so Borch che June 7-, 1955 p FOREIGN PATENTSV i 152550 Great Britain Jan, 8, 922 

1. A PROCESS FOR CARBONIZING AND DISTILLING LIGNITE FOR FORMING COKE AND COAL TAR WHICH COMPRISES HEATING SAID LIGNITE TO DRIVE OFF THE VOLATILE CONSTITUENTS AND TO FORM COKE, AND PASSING SSAID VOLATILE CONSTITUENTS THROUGH A LOCALIZE HEATING ZONE FORMED BY ELECTRICALLY CONDUCTIVE CARBON PARTICLES, PASSING AND ELECTRICAL CURRENT THROUGH CARBON PARTICLES TO HEAT SAID ZONE TO INCANDESCENCE TO CONVERT SAID VOLATILE CONSTITUENTS SO THAT UPON CONDENSATION SAID VOLATILE CONSTITUENTS FORM A COAL TA HAVING THE CHARACTERISTICS OF HIGH-TEMPERATURE TARS. 